One of the longest lasting love stories in nature is also one of the most unique. Not only is this tale about two separate species, the main characters are not even in the same kingdom. One is a plant, the other an animal. Soapweed yucca and the yucca moth have a relationship known as "obligate mutualism" in which one species cannot survive without the other. Over millions of years they have come to an arrangement that allows both to thrive with certain sacrifices from each.